1. Field of the Invention
The present invention relates to a hydrostatic gas bearing for supporting a rotary shaft which is rotating at high speed.
2. Description of the Prior Art
There has been a conventional hydrostatic gas bearing of the above-mentioned type as shown in FIG. 3. The hydrostatic gas bearing has an approximately cylindrical housing 21, a ring-shaped first hydrostatic bearing unit 22 inserted in the housing 21, a ring-shaped spacer 23, and a ring-shaped second hydrostatic bearing unit 24. The first hydrostatic bearing unit 22, spacer 23, and second hydrostatic bearing unit 24 are radially supported on an inner peripheral surface of the housing 21 via O-rings 25 and 25, an O-ring 26, and O-rings 27 and 27, respectively. At the leftmost end in FIG. 3 of the housing 21 is formed an inner peripheral end portion 28, and an inner peripheral surface of the inner peripheral end portion 28 forms a through hole 31 in which a rotary shaft 30 is inserted. An opening portion 32 formed at the rightmost end in FIG. 3 of the housing 21 is engaged with a cover 33. An annular projection 33a which is provided on the cover 33 for pressing use axially supports the second hydrostatic bearing unit 24 to axially support the bearing units 22 and 24 and the spacer 23.
In the above-mentioned hydrostatic gas bearing, the rotary shaft 30 is inserted from the through hole 31 of the housing 21 into a through hole 22a of the bearing unit 22, a through hole 23a of the spacer 23, and a through hole 24a of the bearing unit 24. Then a pressured fluid is made to jet from a nozzle 22b of the bearing unit 22 and a nozzle 24b of the bearing unit 24 to radially support the rotary shaft 30.
However, in the above-mentioned conventional hydrostatic gas bearing, the housing 21 is distorted as shown in FIG. 3. When the opening portion 32 of the housing 21 has an end surface 38 which is not perpendicular to the center axis of the housing 21, the cover 33 is inclined apart from a direction perpendicular to the center axis. Due to the above-mentioned arrangement, the second bearing unit 24 has an excessive axial clearance with respect to a lower portion in FIG. 3, which makes the bearing unit 24 incline to cause an axial center of the bearing unit 24 to incline with respect to the center axis. The above fact results in the problem that the bearing unit 24 cannot obtain an appropriate radial gap with respect to the rotary shaft 30. Furthermore, a gap is generated between the bearing unit 24 and the adjacent spacer 23, and a break of airtightness takes place at the gap to result in the problem that the bearing capability is deteriorated.
In order to correct the inclination of the bearing unit, there has been a conventional technique of adjusting the inclination in assembling by means of a shim or the like, which is accompanied by the problem of increasing the number of processes in assembling of the bearing unit.